1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine.
2. Description of Related Art
There has been known an internal combustion engine which includes an intake-port fuel injection valve for injecting a fuel to an intake port and an in-cylinder fuel injection valve for directly injecting a fuel into a combustion chamber and which changes a fuel injection mode by changing an injection amount ratio between the fuels to be injected from those fuel injection valves according to an engine operation state.
Further, generally, an internal combustion engine is provided with a sensor for outputting an output value corresponding to an oxygen concentration in exhaust gas in order to yield exhaust-gas purification performance of a catalyst provided in an exhaust passage. An air-fuel ratio control of correcting a fuel injection amount so that an output value of the sensor achieves an output value corresponding to a target air-fuel ratio is performed.
In the meantime, it is also known that, even if the air-fuel ratio control is performed, a variation in the air-fuel ratio is caused among cylinders. In view of this, Japanese Patent Application Publication No. 2012-233425 (JP 2012-233425 A) or the like, for example, describes such a technique that, in a case where a variation in an air-fuel ratio is caused among cylinders, it is identified which causes such a variation failure, an intake-port fuel injection valve or an in-cylinder fuel injection valve, and then, a degree of the variation failure is calculated.
When air-fuel ratios of some of the cylinders deviates toward a rich side, for example, relative to air-fuel ratios of the other cylinders, a concentration of hydrogen exhausted from the cylinders increases, so that a sensor for detecting an air-fuel ratio detects hydrogen, thereby resulting in that an output value of the sensor deviates toward a rich side relative to an output value corresponding to an actual air-fuel ratio. This is described in Japanese Patent Application Publication No. 2009-30455 (JP 2009-30455 A), or the like, for example.
When the output value of the sensor deviates toward the rich side as such, a fuel injection amount is wrongly corrected to be decreased in the air-fuel ratio control, so that the actual air-fuel ratio deviates toward a lean side. Accordingly, when a variation occurs among the cylinders and the output value of the sensor for detecting an air-fuel ratio deviates from the actual air-fuel ratio, it is preferable that a target air-fuel ratio be corrected just by a deviation of the output value of the sensor, so as to restrain false correction of the fuel injection amount by the air-fuel ratio control.
Here, the deviation of the output value of the sensor is changed according to a degree of variation among the cylinders. However, in a case of the internal combustion engine including the intake-port fuel injection valve and the in-cylinder fuel injection valve, a degree of variation among the cylinders in terms of a fuel amount to be injected from the intake-port fuel injection valve often differs from a degree of variation among the cylinders in terms of a fuel amount to be injected from the in-cylinder fuel injection valve. Accordingly, unless the aforementioned correction of the target air-fuel ratio to restrain false correction is performed appropriately in accordance with a fuel injection mode, it is difficult to sufficiently restrain the false correction of the fuel injection amount, which may cause an adverse effect on exhaust-gas purification performance.